[llvm] [VPlan] Introduce CSE pass (PR #151872)

[Florian Hahn via llvm-commits]

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@@ -1752,6 +1752,76 @@ void VPlanTransforms::clearReductionWrapFlags(VPlan &Plan) {
   }
 }
 
+/// Hash the underlying data of a VPSingleDefRecipe pointer, instead of hashing
+/// the pointer itself.
+namespace {
+struct VPCSEDenseMapInfo : public DenseMapInfo<VPSingleDefRecipe *> {
+  static bool isSentinel(const VPSingleDefRecipe *Def) {
+    return Def == getEmptyKey() || Def == getTombstoneKey();
+  }
+
+  static bool canHandle(const VPSingleDefRecipe *Def) {
+    return isa<VPInstruction, VPWidenRecipe, VPWidenCastRecipe,
+               VPWidenSelectRecipe, VPHistogramRecipe, VPPartialReductionRecipe,
+               VPReplicateRecipe, VPWidenIntrinsicRecipe>(Def);
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fhahn wrote:

you at least need to skip recipes that may read memory I thin. Otherwise you may reuse the value from an earlier load, which gets modified by a store in between.

if it just has side effects without reading state, that should be fine as we don’t remove the side effect causing recipe.

Probably the only relevant case would be stores, which don’t produce a value to replace.

https://github.com/llvm/llvm-project/pull/151872